fix(billing): 默认关闭 OpenAI 长上下文计费

backend/internal/handler/admin/account_handler.go

@@ -1303,6 +1303,10 @@ func (h *AccountHandler) ApplyOAuthCredentials(c *gin.Context) {
 		response.ErrorFrom(c, infraerrors.BadRequest("NOT_OAUTH", "cannot apply oauth credentials to non-OAuth account"))
 		return
 	}
+	if err := service.ValidateOpenAILongContextBillingExtra(existing.Platform, req.Extra); err != nil {
+		response.ErrorFrom(c, err)
+		return
+	}
 
 	updatedAccount, err := h.adminService.UpdateAccount(ctx, accountID, &service.UpdateAccountInput{
 		Type:        req.Type,